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cardiomac
24-Feb-2012, 22:31
Just finished this LED diffusion head for my Omega D2 enlarger. It entirely replaces the condenser head so you have to use under-the-lens filters. It works pretty well - the light is even and the multi-contrast filters work as expected. I used six Cree XP-E's at 1 ampere which generates about 900 lumens but the white acrylic soaks up about half that so only about 500 lumens hits the negative. The major thing that is not ideal is that the 24 volt power supply takes about 1.9 seconds to come on after plugging it in. The light doesn't ramp up; it just snaps on at full brightness after 1.9 seconds. I've dealt with it by simply adding 2 seconds to the time on the Gra-Lab but it would be nice if that were not necessary. Testing with a step wedge shows contrast is about the same as the condenser head which is surprising - I expected it to be softer. That may be a consequence of the spectrum of these LED's which are a little cooler than an incandescent bulb. The Cree LED's I'm using have a listed color temperature of 3000K. Overall I'm very happy with it and I can't wait to try it out on some real pictures.

ic-racer
24-Feb-2012, 23:57
Beautiful construction, thanks for sharing! Have you tried the timer interrupting the 24V circuit?

Brian C. Miller
25-Feb-2012, 02:26
Excellent! You might consider using a conventional transformer, zener diode, and pi filter for your 24V supply. Those come on instantly, and you won't have to compensate the times.

Doremus Scudder
25-Feb-2012, 03:44
Really pretty! When are you going into production? :)

As for the 1.9 sec. delay, one could just hold a card under the lens till the LEDs came on... If you use the Gralab in count-up mode, you may be able to just add a few "negative seconds," or just pull the card at the 5 second mark and just subtract. I print with a metronome and would just start counting when I pulled the card (I do this often anyway).

Best,

Doremus

cardiomac
25-Feb-2012, 07:22
Beautiful construction, thanks for sharing! Have you tried the timer interrupting the 24V circuit?

Thanks for the compliment. I thought about it but I wanted to keep it really simple and inexpensive. Right now it just uses an off-the-shelf power brick.

cardiomac
25-Feb-2012, 07:42
Excellent! You might consider using a conventional transformer, zener diode, and pi filter for your 24V supply. Those come on instantly, and you won't have to compensate the times.

That's a great idea. I had hoped to avoid making my own power supply because of cost and because I wanted something UL approved on the high voltage side. But you have gotten me thinking. Right now I'm using a desktop switching power supply (Phihong) but that's kind of overkill. I really just need an unregulated linear power supply that supplies anywhere from 20 to 30 volts DC. Current limiting to 1 ampere is done by an LM317 inside the lamp head to take advantage of the heat sink. At 1 ampere the 6 LED's drop about 3 volts each so the voltage will take care of itself. There may still be a short delay as the filtering capacitor in the power supply charges on start-up but as long as it is less than a second or so it will be acceptable. Thanks for the advice.

cardiomac
25-Feb-2012, 07:49
Really pretty! When are you going into production? :)

Thanks. I have a tiny bit more design to do before thinking about selling any of these. And I really want to solve this power-on delay issue. It doesn't really bother me but I'm sure it would annoy the heck out of many other people. But after all these issues are resolved, I was thinking of offering it for $279.00. What do you think?

jeroldharter
27-Feb-2012, 18:15
Thanks. I have a tiny bit more design to do before thinking about selling any of these. And I really want to solve this power-on delay issue. It doesn't really bother me but I'm sure it would annoy the heck out of many other people. But after all these issues are resolved, I was thinking of offering it for $279.00. What do you think?

I think you need an 8x10 version!

Somebody is selling an 8x10 conversion for Beseler 4x5 enlargers that looks like it is made of cardboard and household flourescent bulbs. The LED light source would be nice for that.

Brian C. Miller
27-Feb-2012, 19:02
The problem with an 8x10 version is the column height. Weight-wise, yeah baby! But how far that column can go up with, say, a 240mm lens on it is another problem. The best solution for an Omega 8x10 conversion is to put the new components above the lamp house stage arms, and then fit the lens to a cone. Then nothing gets in the way, and switching back is very easy.

jp
28-Feb-2012, 07:06
Beautiful work. I've never been able to get the crinkle-coat finish like that!

I'd buy one if it could be shown to have an even illumination comparable or better than traditional light sources and if it were for beseler. The vacuum/blower attached to my beseler dichroic head really spoils the tranquility of darkroom work.

As to the timing issue, the easiest thing would be to put a relay between the power supply and the head. Use something with a 120v coil, and you can power it with your existing timer. Something like 220919310097 would replace your timer and provide a relay. I'd put a switch in parallel with this item or your relay to allow override for focusing/composing.

cardiomac
28-Feb-2012, 09:42
Beautiful work. I've never been able to get the crinkle-coat finish like that!

Thanks. I'm using Krylon brand paint and lay on two thick coats before putting the parts in an oven at 170 degrees F. The paint wrinkles in about 10 minutes but takes about 3 hours in the oven to cure fully. The marred finish near the heatsink was caused by silicone heatsink compound. I've figured out a way to avoid this in the future. In this prototype the heatsink is not painted but in future models it will be. The slight loss of heat transfer that results from the paint will be made up for by enlarging the heatsink. I tried it with a painted heatsink and it looks stunning!


I'd buy one if it could be shown to have an even illumination comparable or better than traditional light sources and if it were for beseler. The vacuum/blower attached to my beseler dichroic head really spoils the tranquility of darkroom work.

The evenness of illumination appears to be nearly perfect, both by meter and by exposing paper with no negative in the enlarger. This took some doing because it is non-intuitive. One would think that simply spacing the LED's evenly would be sufficient but it is not, at least not in the enclosure I'm using. No fan is needed. Purposely leaving the LED's on continuously for an hour causes only a modest warming of the heatsink. Unfortunately, I still don't have access to a Beseler to make something for that enlarger, but it is on the agenda because Beseler's are so popular.


As to the timing issue, the easiest thing would be to put a relay between the power supply and the head. Use something with a 120v coil, and you can power it with your existing timer. Something like 220919310097 would replace your timer and provide a relay. I'd put a switch in parallel with this item or your relay to allow override for focusing/composing.

It is easy to do but to limit legal liability I want everything electrical to be UL approved, especially on the high-voltage side.

Thanks again for your comments.

jp
28-Feb-2012, 15:19
If you could stick to a time schedule for it's return, I'd send you my beseler 4x5 dichroic head for a couple weeks if you wanted to do that sort of project. Sending a whole enlarger would be difficult.

A larger load or smaller power supply might reduce the 2s delay you speak of.

Sell it "power supply optional", and people will figure out a way to time it. Or have someone overseas sell a relay interface. Without a relay, instead of a power input jack on the head, you could have a remote cabled box for the power input from the power supply and a pushbutton & toggleswitch to operate the head. Probably an extra $20 that way

cardiomac
28-Feb-2012, 17:18
If you could stick to a time schedule for it's return, I'd send you my beseler 4x5 dichroic head for a couple weeks if you wanted to do that sort of project. Sending a whole enlarger would be difficult.

A larger load or smaller power supply might reduce the 2s delay you speak of.

Sell it "power supply optional", and people will figure out a way to time it. Or have someone overseas sell a relay interface. Without a relay, instead of a power input jack on the head, you could have a remote cabled box for the power input from the power supply and a pushbutton & toggleswitch to operate the head. Probably an extra $20 that way

Thanks for the offer. I may take you up on it in a few weeks after I've gotten all the kinks worked out of this project.

cardiomac
29-Feb-2012, 20:18
Problem solved! I replaced the switching power supply with a transformer power supply and the lamps now come on virtually instantaneously! With this problem solved I'm going to go ahead build a few units for sale. The only parts I lack are the machined aluminum pieces. It will take about two weeks to receive them from the shop. Finished units should be available in three or four weeks. After that I'll start on something for the Beseler 45.

Roger Cole
29-Feb-2012, 22:33
I have one of his first LED lamphouses and it works great. I need to find a box and send it back because he's offering to upgrade it with the latest changes for free. :) I did some testing compared to my incandescent lamphouse and can see no difference between them in evenness or contrast. The LED is just about exactly between a 75W 211 and a 150W 212 bulb in printing speed. I made some exposures with no negative for comparison but I'm on my iPhone now and don't have access to them.

I wish there were some way to use above lens filters though. I just replaced my faded ones for neatly $60 and would have to get a new set AND keep them clean AND get the filter rod holder thingy for all my lensboards, or swap one around.

Fotch
2-Mar-2012, 11:01
I would be interested in your Beseler 45 model.